1. Field of the Invention
The present invention relates to a blade type focal plane shutter.
2. Description of the Prior Art
Heretofore a focal plane shutter, which effects shutter operation by parallel-linked movements of shutter blades made of a plurality of opaque thin plates and two operating arms supporting the blades, has been used in a single lens reflex camera, etc., and has been generally known.
Such shutters, however, are required to have a small size so that the size of a camera, especially the height thereof can be reduced to a low level.
Therefore, in a shutter having such an arrangement the leading blade group and the trailing blade group are made of a number of blades respectively and the width of a portion at which the blades are housed in a folded manner between the view finder eyepiece part and the exposure window of a camera is made narrow while connecting parts between the shutter blades and the operating arms are made to have large widths and are housed at a side of the view finder eyepiece part. FIG. 1 and FIG. 2 show an example of a blade type focal plane shutter made to have a small size as mentioned above.
In FIG. 1,
In FIG. 1, there is shown a shutter comprising a view finder eyepiece part 1, a shutter base plate 2, and an exposure window 3 of the shutter base plate 2. A leading blade group A is positioned at a lower part, and a trailing blade group B is positioned at an upper part. Blades with opaque thin plates and operating arms constituting the leading and trailing blade groups A and B respectively have symmetrical structures and therefore similar parts are identified with similar reference characters, and respectively comprise slit forming blades 4 and first to fourth auxiliary blades 5, 6, 7, 8 which succeed the same, making a total of five blades. Operating arms 9, 10 are rotatable around shafts 11, 12 provided at a side of the exposure window 3 in the base plate 2, respectively, and rotatably supporting the slit forming blades 4 by pins 9a, 10a provided at the fore ends thereof. The shafts 11, 12 and pins 9a, 10a are positioned to form a parallelogram. The first auxiliary blade 5 succeeding the slit forming blade is pivotally supported by pins 9b, 10b provided at positions on the operating arms 9, 10 closer to the shafts 11, 12 than the pins 9a, 10a , and thus these blades and succeeding second to fourth blades, 6, 7, 8 are supported respectively by rotating pins 9a, 9b, 9c, 9d, 9e as well as 10a, 10b, 10c, 10d, 10e mounted at positions closer to the shafts 11, 12. The blade groups A and B will respectively make parallel-linked movements as the operating arms 9, 10 rotate by a movement of a driving pin (not shown) inserted into a hole 10f repectively provided in the operating arm 10.
The state shown in FIG. 1 is such that the trailing blade group B is folded up at the upper part and the leading blade group A makes a parallel movement downwards so that a portion of the exposure window 3 in the shutter base plate 2 begins to be exposed.
The most difficult problem in reducing the size of a blade type focal plane shutter of this kind of parallel-linked movement system concerns the manner in which the first auxiliary blade 5 which succeeds the slit forming blade 4 is supported. That is, while the first auxiliary blade 5 is supported at the operating arms 9, 10 respectively by the rotating pins 9b, 10b, especially for preventing the rotation pin 9b from striking the slit forming blade 4, a notched part 4a forming an escapement for the rotation pin 9b must be provided on the slit forming blade 4 as shown in FIG. 2, which shows a relationship between the slit forming blade 4 of the leading blade group A and the operating arm 9 thereof. And while the distance between the rotation pins 9a and 9b may be made large in order to reduce the amount of the escapement, the position of the rotation pin 9b is limited in connection with a moving distance (stroke) of the blades.
Therefore, heretofore, the distance between the rotation pin 9a and the rotation pin 9b has been, along with sizes of the supporting spans for the operating arms 9, 10, made as long as possible and at the same time the position of the rotation pin 9b is set so as to be shifted to the counterclockwise direction in the drawing around the rotation pin 9a so that a tail part 4b is left at the left end of the slit forming blade 4. Also, a protruding part 4c is formed for supporting the rotation pin 10a at a position shifted to the clockwise direction. Therefore, any defect will not be generated in the slit forming part and the escapement of the rotation pin 9b can be made small, whereby there will be no gaps generated between blades in the course of an operation.
The protruding part 4c is housed in a space below the exposure window under a state in which the leading blade group A is folded downwards, while that for the trailing blade group is housed in a space in a shoulder part 13 of the base plate 2 when the trailing blade group is folded upwards.
Now, in order to reduce the size of this kind of blade type focal plane shutter, the space of the shoulder part 13 should not be used, but for that end the above-mentioned protruding part 4c should not be present at the slit forming blade 4. However, when the protruding part 4c is not provided at the slit forming blade 4, the position of the rotation pin 10a is unavoidably located at an upper area compared to the position shown in FIG. 2, and along with the same the positions of the rotation pin 10b and the rotation pin 9b move to upper positions. Since a parallelogram must be formed together with the rotation pin 10a and the rotation pin 9a, in order to prevent the rotation pin 9b from striking the tail part 4b at the left end of the slit forming blade 4 in FIG. 2 when the leading blade group A moves downwards, the tail portion 4b needs to be cut off and the escapement provided by the notched part 4a becomes large. Accordingly, there will be a disadvantage in that a complete slit part cannot be formed between both blade groups at the time of an exposure and an exposure window can-not be completely covered during the blade operation, causing leakage of light.